1. Technical Field of the Invention
The present invention relates circuits and, more particular, to transistor group mismatch detection and reduction.
2. Background Art
The performance of a transistor includes the rate at which the transistor can switch states. The performance of an integrated circuit (also called a chip or die) is related the clock frequency, which may be limited by transistor switching speed. Other parameters of an integrated circuit include its temperature and power consumption. If the chip temperature is above a maximum, the transistor might not properly switch or retain its state. The performance, power consumption, and temperature are typically related. The active power of a transistor is P=CV.sup.2 F, where C is the capacitance, V is the supply voltage, and F is the switching frequency. For example, transistors with a greater switching rate, consume energy in a shorter period of time, which generates heat over a smaller period of time thereby increasing the temperature of the chip. If the clock frequency and programs being run are such that a high switching rate is sustained, the temperature may be so high that thermal reduction mechanisms are not adequate.
For example, consider a portable computer (such as a handheld or laptop computer) that includes a processor such as a Pentium.RTM. II processor manufactured by Intel Corporation. The temperature of the processor chip may be a function of the switching rate of the transistors, the clock frequency, and the program being run by the computer. Word processing programs tend to make relatively little demands on the processor while the user is doing tasks such as editing and printing. Accordingly, even if the transistors have a relatively high switching rate and clock rate, when running only a word processing program, the temperature of the chip will not exceed a particular temperature limit. By contrast, when running certain other programs (such as games or other programs involving extensive computations for 3D graphics), or a combination of programs in multi-tasking, the processor may be required to sustain a high rate of transistor switching per unit time leading to substantial power consumption and resulting temperature increase. The heat generated by the processor over this time may be greater than the computer thermal reduction mechanism can deal with leading to overheating of the processor and perhaps other portions of the computer.
The switching rate can also lead to an increase in power consumption rate because more instructions can be executed in a shorter amount of time. This is particularly a problem with battery driven processors.